Fig. 4B illustrated the effect of operating potential on the amperometric
signals of CC (curve b), HQ (curve c) and the background
current (curve a) in the range between
−400 and 100 mV. For CC,
when the applied potential was more negative than
−200 mV, a
higher signal current was achieved, however, the background current
also increased. Therefore, an applied potential of
−200 mV
was selected for the amperometric measurements. Similarly, the
optimal potential for HQ was
−150 mV. Moreover, the low applied
potentials were beneficial to minimize the interferences from the
coexisting electro-active material.